1. Field of the Invention
This invention relates to optical microscopy. More particularly, it relates to far-field resonance fluorescence localization microscopy.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
The resolution limit of traditional far-field optical microscopy is about half the wavelength of the light [see, e.g., E. Abbe, Arch. Mikr. Anat. 9, 413 (1873) and L. Rayleigh, Philos. Mag. 47, 81 (1874)]. To achieve better resolution, one must switch to shorter wavelengths (e.g., electron microscopy) which is usually invasive to the system [see, e.g., A. Diaspro (ed), Nanoscopy and Multidimensional Optical Fluorescence Microscopy (CRC Press, Boca Raton, 2010)]. Near-field scanning microscopy can obtain optical imaging with sub-diffraction resolution [see, e.g., G. Binnig, C. F. Quate, and C. Gerber, Phys. Rev. Lett. 56, 930 (1986) and C. Hettich et al., Science 298, 385 (2002)], but due to the surface bound nature it is limited in application. Two-photon fluorescence microscopy first was developed to achieve a higher resolution than classical one-photon fluorescence microscopy in the far field [see, e.g., W. Denk, J. H. Strickler, and W. W. Webb, Science 248, 73 (1990) and J. H. Strickler and W. W. Webb, Proc. SPIE 1398, 107 (1991)]. Stimulated emission depletion (STED) and the related concept of ground-state depletion microscopy are then developed to overcome the far-field diffraction limit in fluorescence microscopy [see, e.g., S. W. Hell and J. Wichmann, Opt. Lett. 19, 780 (1994) and S. W. Hell and M. Kroug, Appl. Phys. B 60, 495 (1995)]. Space-dependent dark states are also proposed to achieve subwavelength resolution [see, e.g., G. S. Agarwal and K. T. Kapale, J. Phys. B 39, 3437 (2006) and S. Bretschneider, C. Eggeling, and S. W. Hell, Phys. Rev. Lett. 98, 218103 (2007)]. However, realization of these schemes is based on point-by-point scanning and is time consuming. Coherent Rabi oscillations may also be employed to break the diffraction limit [see, e.g., Z. Liao, M. Al-Amri, and M. S. Zubairy, Phys. Rev. Lett. 105, 183601 (2010) and C. Shin et al., J. Lumin. 130, 1635 (2010)], but the effect of dipole-dipole interaction has not been well discussed. Another method based on resonance fluorescence is able to measure the separation of two interacting atoms with subwavelength resolution [see, e.g., J-T Chang, J. Evers, M. O. Scully, and M. S. Zubairy, Phys. Rev. A 73, 031803(R) (2006) and Q. Sun, M. Al-Amri, M. O. Scully, and M. S. Zubairy, Phys. Rev. A 83, 063818 (2011)].
A question remains whether the locations of multiple atoms can be determined with sub-wavelength resolution even when dipole-dipole interaction is involved.